Sialylated oligosaccharide and sialic acid profile of colostrum, transition milk, and whole milk in primiparous and multiparous Holstein dairy cattle.
The objective of this study was to characterize the sialylated oligosaccharide (OS) and sialic acid (SA) profile during the first week of lactation in primi- (PP) and multi-parous (MP) dairy cattle. The animal experiment consisted of MP (n = 10) and PP (n = 10) Holstein dairy cows assigned to the study at the time of calving. Colostrum (milking 1) and milk (milkings 2–4, 8, and 14) samples were collected twice daily. Oligosaccharides were quantified by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection and HPLC-MS/MS. Median OS levels were deemed statistically significant if 2-tailed Mann-Whitney U values were lower than Ucrit at P < 0.05 or 0.01, while differences in OS levels between parity were assessed using a 2-tailed Student’s t test with P < 0.05 considered significant. Total SA were quantified by HPLC-MS after cleavage from milk OS or glycoproteins by weak acid hydrolysis and evaluated using a Wilcoxon rank test with P < 0.05 considered significant. A total of 9 SA were quantitated, including 5-N-acetylneuraminic acid (Neu5Ac), N-glycolneuraminic acid (Neu5Gc), and 7 O-acetylated analogs; 2-keto-3-deoxy- D-glycero-D-galacto-nonulsonic acid (Kdn). A 4-fold decrease in concentrations of both OS- and glycoprotein-bound SA over the first 14 milkings was observed. Median levels of OS-bound Neu5Ac increased (P < 0.001) from 58 to 79% of total SA to the decrement of Neu5Gc (14 to 7%) and Kdn (28 to 17%) (P < 0.001). Cow parity influenced levels of specific SA species at milking 14 (P < 0.005), but not in colostrum (P > 0.08). The absolute levels of sialylated OS decreased (P < 0.002) from milking 1 to 14. While total OS levels slightly decreased from milking 1 to 14, relative levels of at least 10 sulfated OS increased over 3-fold (10 vs. 35%; P < 0.03) and were inversely correlated with sialic acid-containing milk OS. Future research should characterize how the observed marked changes in OS biosynthetic pathways during the early postpartum period may influence the newborn calf microbiome and immune system.